How to set ringtone in Android to downloaded audio? [duplicate]

Possible Duplicate:

How to set ringtone in Android from my activity?

What I want to do in my app is to cre开发者_如何学JAVAate a single button, and whenever that button is pressed, I want the audio to be downloaded and set it as a ringtone when the download is finished. But the problem is, I really don't know how to set the download object as a ringtone. I know how to download audio.

Hopefully not possible, as that would be quite disturbing if an app could just change your ringtone. But then again, I haven't intensively studied the subject so I can't tell for sure.